A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form.
Certain devices within the network referred to as routers use routing protocols to exchange and accumulate topology information that describes the network. This allows a router to construct its own routing topology map of the network. Upon receiving an incoming data packet, the router examines keying information within the packet and forwards the packet in accordance with the accumulated topology information.
Many routing protocols use flooding-based distribution mechanisms to announce topology information to routers within the network. These routing protocols typically rely on routing algorithms that require each of the routers to have synchronized routing topology information. That is, flooding-based routing protocols require that all routers in the routing domain store all of the routing information that has been distributed according to the protocol. In this way, the routers are able to select routes that are consistent and loop-free. Further, the ubiquity of the routing information allows the flooding process to be reliable, efficient and guaranteed to terminate. In operation, each router typically maintains an internal link state database and scans the entire database at a defined interval to generate and output link state messages so as to synchronize the database to neighboring routers within the routing domain. In this way, link state is propagated across the entire routing domain and stored in full at each router within the domain.
For example, Open Shortest Path First (OSPF) and Intermediate system to intermediate system (IS-IS) routing protocols are link state protocols that use link state messages to ensure their routing topology is synchronized with respect to available interfaces, metrics and other variables associated with network links. OSPF utilizes Link State Advertisements (LSAs) while IS-IS uses Link State Protocol Data Units (LSPs) to exchange information. A router generating a link state message typically floods the link state message throughout the network such that every other router receives the link state message. In network topologies where routers are connected by point-to-point connections, each router floods link state messages to adjacent routers reachable on each interface to ensure synchronization. In networks using multi-access media, such as an Ethernet network, the routers within the network flood the link state messages to all other routers. In either case, the receiving routers construct and maintain their own network topologies using the link information received via the link state messages. IS-IS is specified in “Intermediate system to Intermediate system routing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473),” ISO, ISO/IEC 10589:2002, the entire contents of which is incorporated herein by reference.
Recently, flooding-based routing protocols have been extended to carry significant information between routers that is ancillary to routing control. For example, in addition to carrying topology information, routing protocols have been extended to carry implementation-specific information, such as configuration data, hardware inventory, additional capability information and other information.